1. Field of the Invention
The present invention relates to a capacitor configuration in an integrated circuit ("IC"), and more particularly, to a configuration adapted to being manufactured using many of the same process steps as in the manufacture of floating gate transistors.
2. Description of Related Art
Capacitors are found in memory circuits and other large scale integrated circuits. Capacitors hold a charge, due to the presence of dielectric material between layers of conductive material. Capacitors have been formed in integrated circuits on substrate in various configurations, including so-called MOS-capacitors and well-capacitors.
The cost of manufacturing integrated circuits depends, in part, upon the number of process steps required and upon the area of the components. Therefore, it is desirable to use the same process steps to create capacitors as are used to manufacture other IC components, such as floating gate transistors. Also, it is desirable to provide capacitors having relatively higher capacitance per unit area on the chip. The details of such process steps can be seen upon review of the following U.S. Patents which are incorporated by reference:
Yiu, et al, U.S. Pat. No. 5,399,891 issued Mar. 21, 1995; PA1 Yiu, et al., U.S. Pat. No. 5,453,391 issued Sep. 26, 1995; PA1 Chang, et al., U.S. Pat. No. 5,619,052 issued Apr. 8, 1997; PA1 Yiu, et al., U.S. Pat. No. 5,633,185 issued May 27, 1997; PA1 Takeuchi, U.S. Pat. No. 5,661,056 issued Aug. 26, 1997; and PA1 Chang, U.S. Pat. No. 5,763,309 issued Jun. 9, 1998. A non-planer IC structure which incorporates a capacitor is described in Brown, W., Brewer, J. eds., Nonvolatile Semiconductor Memory Technology, published by IEEE Press 1997, Ch. 3, pp. 157-158.
Increased surface area of the conductive material on either side of a dielectric increases the available capacitance of a device. At the same time, increased surface area of horizontal capacitor plates decreases the density of devices on the IC and increases cost. This concern about the density of devices has led to trench capacitor designs. Generally, it is desirable to minimize the footprint or the surface area of horizontal capacitor plates.
Parasitic capacitance is inherent in the construction of IC devices on a substrate. In the design of a capacitor, it is desirable for the parasitic capacitance to be small in relationship to the design capacitance.